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Previously the srch compaction work would output the entire compacted file and delete the input files in one atomic commit. The server would send the input files and an allocator to the client, and the client would send back an output file and an allocator that included the deletion of the input files. The server would merge in the allocator and replace the input file items with the output file item. Doing it this way required giving an enormous allocation pool to the client in a radix, which would deal with recursive operations (allocating from and freeing to the radix that is being modified). We no longer have the radix allocator, and we use single block avail/free lists instead of recursively modifying the btrees with free extent items. The compaction RPC needs to work with a finite amount of allocator resources that can be stored in an alloc list block. The compaction work now does a fixed amount of work and a compaction operation spans multiple work iterations. A single compaction struct is now sent between the client and server in the get_compact and commit_compact messages. The client records any partial progress in the struct. The server writes that position into PENDING items. It first searchs for pending items to give to clients before searching for files to start a new compaction operation. The compact struct has flags to indicate whether the output file is being written or the input files are being deleted. The server manages the flags and sets the input file deletion flag only once the result of the compaction has been reflected in the btree items which record srch files. We added the progress fields to the compaction struct, making it even bigger than it already was, so we take the time to allocate them rather than declaring them on the stack. It's worth mentioning that each operation now takes a reasonably bounded amount of time will make it feasible to decide that it has failed and needs to be fenced. Signed-off-by: Zach Brown <zab@versity.com>
Introduction
scoutfs is a clustered in-kernel Linux filesystem designed and built from the ground up to support large archival systems.
Its key differentiating features are:
- Integrated consistent indexing accelerates archival maintenance operations
- Log-structured commits allow nodes to write concurrently without contention
It meets best of breed expectations:
- Fully consistent POSIX semantics between nodes
- Rich metadata to ensure the integrity of metadata references
- Atomic transactions to maintain consistent persistent structures
- First class kernel implementation for high performance and low latency
- Open GPLv2 implementation
Learn more in the white paper.
Current Status
Alpha Open Source Development
scoutfs is under heavy active development. We're developing it in the open to give the community an opportunity to affect the design and implementation.
The core architectural design elements are in place. Much surrounding functionality hasn't been implemented. It's appropriate for early adopters and interested developers, not for production use.
In that vein, expect significant incompatible changes to both the format of network messages and persistent structures. To avoid mistakes the implementation currently calculates a hash of the format and ioctl header files in the source tree. The kernel module will refuse to mount a volume created by userspace utilities with a mismatched hash, and it will refuse to connect to a remote node with a mismatched hash. This means having to unmount, mkfs, and remount everything across many functional changes. Once the format is nailed down we'll wire up forward and back compat machinery and remove this temporary safety measure.
The current kernel module is developed against the RHEL/CentOS 7.x kernel to minimize the friction of developing and testing with partners' existing infrastructure. Once we're happy with the design we'll shift development to the upstream kernel while maintaining distro compatibility branches.
Community Mailing List
Please join us on the open scoutfs-devel@scoutfs.org mailing list hosted on Google Groups for all discussion of scoutfs.
Quick Start
This following a very rough example of the procedure to get up and running, experience will be needed to fill in the gaps. We're happy to help on the mailing list.
The requirements for running scoutfs on a small cluster are:
- One or more nodes running x86-64 CentOS/RHEL 7.4 (or 7.3)
- Access to a single shared block device
- IPv4 connectivity between the nodes
The steps for getting scoutfs mounted and operational are:
- Get the kernel module running on the nodes
- Make a new filesystem on the device with the userspace utilities
- Mount the device on all the nodes
In this example we run all of these commands on three nodes. The block device name is the same on all the nodes.
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Get the Kernel Module and Userspace Binaries
- Either use snapshot RPMs built from git by Versity:
rpm -i https://scoutfs.s3-us-west-2.amazonaws.com/scoutfs-repo-0.0.1-1.el7_4.noarch.rpm yum install scoutfs-utils kmod-scoutfs- Or use the binaries built from checked out git repositories:
yum install kernel-devel git clone git@github.com:versity/scoutfs-kmod-dev.git make -C scoutfs-kmod-dev module modprobe libcrc32c insmod scoutfs-kmod-dev/src/scoutfs.ko git clone git@github.com:versity/scoutfs-utils-dev.git make -C scoutfs-utils-dev alias scoutfs=$PWD/scoutfs-utils-dev/src/scoutfs -
Make a New Filesystem (destroys contents, no questions asked)
We specify that two of our three nodes must be present to form a quorum for the system to function.
scoutfs mkfs -Q 2 /dev/shared_block_device -
Mount the Filesystem
Each mounting node provides its local IP address on which it will run an internal server for the other mounts if it is elected the leader by the quorum.
mkdir /mnt/scoutfs mount -t scoutfs -o server_addr=$NODE_ADDR /dev/shared_block_device /mnt/scoutfs -
For Kicks, Observe the Metadata Change Index
The
meta_seqindex tracks the inodes that are changed in each transaction.scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs touch /mnt/scoutfs/one; sync scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs touch /mnt/scoutfs/two; sync scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs touch /mnt/scoutfs/one; sync scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs